1. Field of the Invention
The present invention relates to a packet forwarding apparatus, and more particularly, to a packet forwarding apparatus applicable to a wide area Ethernet network in which extended Ethernet (registered trademark) frames such as MAC-in-MAC frames are forwarded.
2. Related Art
With the spread of constructing intranets utilizing the Internet technology, a wide area network (WAN) for connecting a local area network (LAN) with another LAN has become widespread. The WAN started services at relatively high cost due to the use of low-speed telephone lines and dedicated lines. However, with the spread of high-speed XDSL and optical links, the WAN became able to provide services at low cost.
At the beginning, a user who wishes to use a communication protocol other than IP (Internet Protocol) in the WAN had to perform personally such a specific processing as protocol conversion, because IP was exclusively used as a communication protocol in the WAN. Thereafter, with the spread of VLAN (Virtual LAN) technology allowing a user to flexibly configure a network, there has been an increasing need for directly forwarding Ethernet frames on the WAN.
Under such circumstances, a wide area Ethernet service network capable of forwarding an Ethernet frame as it is has appeared. For example, as reported in NTT Technical Journal, January 2006, an extended VLAN defined in the next-generation wide-area Ethernet standard IEEE 802.1ah makes it possible to logically bind a plurality of users' VLANs on one network provided by a common carrier, by assigning an individual VLAN-ID to each user's VLAN. However, according to the extended VLAN scheme, users more than 4096 cannot be accommodated in one network. Further, when the number of users increases and the number of MAC addresses exceeds a limit value that can be processed by a layer 2 switch (L2SW) constituting the wide area Ethernet network, the L2SW disadvantageously loses frame forwarding function about specific users.
As one of technologies for solving these problems, a MAC-in-MAC scheme proposed in IEEE 802.1ah is known, as reported in NTT Technical Journal, April 2006, an outline of IEEE 802.1ah provider backbone bridge. The MAC-in-MAC scheme can increase the number of available VLAN-IDs by encapsulating an extended VLAN frame with an Ethernet header to convert it into a MAC-in-MAC frame. Further, by unifying a plurality of MAC addresses to be used individually by a plurality of users into one MAC address with the header of a MAC-in-MAC frame, the MAC-in-MAC scheme enables the L2SW to forward increased number of frames.